functional/fusion/at.hpp

0001 ///////////////////////////////////////////////////////////////////////////////
0002 /// \file at.hpp
0003 /// Proto callables Fusion at
0004 //
0005 //  Copyright 2010 Eric Niebler. Distributed under the Boost
0006 //  Software License, Version 1.0. (See accompanying file
0007 //  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
0008
0009 #ifndef BOOST_PROTO_FUNCTIONAL_FUSION_AT_HPP_EAN_11_27_2010
0010 #define BOOST_PROTO_FUNCTIONAL_FUSION_AT_HPP_EAN_11_27_2010
0011
0012 #include <boost/type_traits/add_const.hpp>
0013 #include <boost/type_traits/remove_const.hpp>
0014 #include <boost/type_traits/remove_reference.hpp>
0015 #include <boost/fusion/include/at.hpp>
0016 #include <boost/proto/proto_fwd.hpp>
0017
0018 namespace boost { namespace proto { namespace functional
0019 {
0020     /// \brief A PolymorphicFunctionObject type that invokes the
0021     /// \c fusion::at() accessor on its argument.
0022     ///
0023     /// A PolymorphicFunctionObject type that invokes the
0024     /// \c fusion::at() accessor on its argument.
0025     struct at
0026     {
0027         BOOST_PROTO_CALLABLE()
0028
0029         template<typename Sig>
0030         struct result;
0031
0032         template<typename This, typename Seq, typename N>
0033         struct result<This(Seq, N)>
0034           : fusion::result_of::at<
0035                 typename boost::remove_reference<Seq>::type
0036               , typename boost::remove_const<typename boost::remove_reference<N>::type>::type
0037             >
0038         {};
0039
0040         template<typename Seq, typename N>
0041         typename fusion::result_of::at<Seq, N>::type
0042         operator ()(Seq &seq, N const & BOOST_PROTO_DISABLE_IF_IS_CONST(Seq)) const
0043         {
0044             return fusion::at<N>(seq);
0045         }
0046
0047         template<typename Seq, typename N>
0048         typename fusion::result_of::at<Seq const, N>::type
0049         operator ()(Seq const &seq, N const &) const
0050         {
0051             return fusion::at<N>(seq);
0052         }
0053     };
0054 }}}
0055
0056 #endif